KLX250 300cc Kit a success Mild to Wild

Kawasaki KLX250 300cc Big Bore Kit (Mild to Wild)
On a recent trip back to Aussie, I called into the local Kawasaki dealer. I have known the owner over the years and most of his staff race Kwakas either on or off road.

I was interested in the 300cc conversion kit for the KLX250. In Aussie, USA, Canada and parts of Europe they are imported with the Keihin 34mm Carby, which passes the strict Californian emission laws.

I used my good friend Liam, an ex racer and motorcycle mechanic from Ireland and now residing in San Sai, Chiang Mai to do the conversion.
He specialises in suspension setups, carby balancing, motor strip downs and general maintenance
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You can contact him on 0822711923
Email: [email protected]
GPS Coordinates: N18deg 50.419 E099deg02.897

After a week of trial, error and frustration we got the little beast to really fly, (a few wee secrets were learned along the way, which Liam will keep to himself!)

Remember we are converting a fuel injected bike back to a carby, then upgrading to a 300cc big bore kit. It is also a brand new bike with a 1000km in the speedo (I guess I now have voided my warrantee!)

Hi all that are interested in history.
I was competing in 3-6day enduros for 5 years from 1972 in OZ.
A lot younger then (early 20's)
I was a privateir (I paid for bike and all costs)
In 5 years I was only deamed a non finisher once.
(not fast,but I last)

Now the reason for this thread.

In 2011 a Kawasaki KLX knocks out 18hp and peaks out at around 120km/hr in top gear with a 7ltr tank(carburated versions outside of SE Asia)

These are the bikes I campained with in 2,3 and 6 day enduros in the early 70's.

In most respects they where as reliable and simpler and easier to ride than their 'modern cousins'.

The current KLX250 sold in Thailand and SE Asia with fuel injection, a relatevly small market is definately underpowered.
Check out the net if you are after more HP for the Kwaka KLX250....Power/hp costs money, there is no easy fix.

Interesting project!
I've noticed that you're not using a different cam; are you using the stock cam with the 300cc set-up? No changes in the cylinder head, valves, valve springs etc?
I don't know much about engines but have heard that just by polishing the head and some hotter cams you can gain a few horses. Not as much as with a bigger bore, of course.
How does the 300cc compare to the 250?

Well Liam and I have completed stage 2.
It took over a month to fine tune the carb, different jetting and needle settings were tried around the mountains, a lot of popping high up because of the altitude.
We finally got a good compromise with the settings.

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Good nice colour

We then fitted the IMS plastic tank from the US, complete with the US carby versions fuel **** system

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This is the IMS tank fitted

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The finished look

I now have a KLX that can cruise on 110km/hr. with a range of 200+km before reserve.
I am sitting on the optimum rev range for power and torque: 7000/8000 rpm with enough power to pass traffic.

I have also saved over 5kg of weight by shedding the emission control and the the fuel injection mechanics.

Liam didn't have to alter any of the wiring loom, just blanked off connections and looped around the CPU.

If in the future I wish to go back to the fuel injection it will only take about 8 hrs work.

I Love that Tank! I saw it in the flesh the other day and You could hardly notice the Change! Very well done without going overboard like those Huge Exon Valdez Tanks that Look so Grotesque!!! Can't Wait till they make one for the Fuel Injected Bikes!

Hi Tom. Could you say how you think this compares re. total price and performance against fitting other carb/EFI big bore conversion kits please. Also a list of sources with prices for the parts would be handy for those wishing to copy you. Cheers.

I am soon to move to Chiang Mai for a number of years and I am fairly set on getting a KLX250. In addition to that I am very interested in the 300 Big Bore kit for the bike. Would you be willing to give us a ballpark figure of what it cost?

TJ, if you are willing to spend the money go for a Kustom Kraft or Bill Blue 331 kit, still can use standard cams and injector (EFI) but will need a decent pipe and remove the airbox cover. The FMF mega bomp and Q4 pipe work well, would also recommend a Power Commander EFI unit and the auto-tune unit. Combination works well, there a few bikes now running these combo's with no issues.

KLX331 Crazy;290668 wrote: TJ, if you are willing to spend the money go for a Kustom Kraft or Bill Blue 331 kit, still can use standard cams and injector (EFI) but will need a decent pipe and remove the airbox cover.

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+1 on that.

IMO spending a lot of money & time on upgrading a small capacity engine to be a little bit bigger, may not be pound for pound your best option!

The klx300 = 292cc ......... The KK or BB 331kits = 331cc. I think 82cc is a significant boost & well worth the extra money over the cost of a klx300 jug & piston.

I know a few guys on other forums that took the easier/cheaper klx300 option before it was proven the 331 option actually worked. Two of the guys have just learnt to live with their mistake & the other just ordered the kk331 kit a few weeks ago.

Whatever jug size you choose a fuel controller will be necessary. EJK [Dobeck Performance] make a very simple plug n play box & they can pre-program it to suit 292 or 331 before sending it to you. The PCv [Power Commander 5] is also a good option.

Suchis Shop is good for all the Bike Gear, Bars, Risers, Bark Busters etc. They have different Quality so make sure You ask for the Best Quality! Bash Plate ask at Kawasaki. Suchis shop is located on Sri Donchai Road. If You go down it from the Moat heading towards Panthip Plaza it is on Your Left about 3/4 of the way down. Just go slow. It Looks like an Old Thai Market Shop with lots of Helmets and stuff hanging outside but if You go in it is stacked to the Roof with all sorts of Gear! He speaks English and has some top notch Jackets as well. Well worth taking a look at. Good Luck.

TJWally;292792 wrote: Hi guys, I am now settled in Chiang Mai and picking up my work permit tomorrow so I will be picking a klx up asap!

Anyone know where is a good place to get accessories? Such as bars, risers, bark busters, bashplate????

Have no idea where to start looking apart from the kawasaki shop and I am supposing that is going to be dead expensive.

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If you turn left from the moat at Mikes Burgers and head down towards China town about 200 meters before u get there look out for a double shop on the left that carries a huge range of accessories for almost everything. Their prices are good and they will fit almost everything immediately for no extra charge. I cant remember the name of it.

Hi All, I am new to this forum and have recently sold my Versys and "down graded" to a KLX 250 2011 Model. I have decided to take the risk in doing adventure riding around Thailand on a much smaller cc bike and i hope some of you here can give me some tips. Since i will be doing adventure riding from Malaysia, the top priority for me is an after market gas tank. I have my eye on the 3gal IMS tank but changing the tank also means i need to convert the bike from EFI to Carburetor (it really sucks that the EFI model have been around for a few years now and no after market gas tank for it).

I know some of you have done the mods from EFI to Carburetor, most notably Tom who started this thread but if there are others who have done such conversion from EFI to Carburetor please feedback on the performance of the bike after the conversion. Also, is the conversion a difficult thing to do? Will it cause problems later? The last thing i want is to breakdown in the middle of nowhere. I have decided to go with the Bill Blue 331 Big Bore Kit together with the Mikuni TM33 which Bill also sells. Have anyone installed a BB Kit? Are there any reliability issues? Jetting issues? Fuel flow issues? Hope to hear from all of you. Thanks in advance.

I've got the Bill Blue 351 big bore paired with a Mikuni TM33 carb and a 3 gallon (11.3 liter) IMS tank and am super happy with the set-up. Very easy to service and tune and I get about the same range with the IMS that my mates do with the small stock tank and 100cc's less displacement. Bill Blue's kits have an excellent reputation and Mikuni carbs are top quality and very easy to set up.{}

Thanks a lot for your feedback and reassuring me about Bill Blue BB Kit, thats my main option to pair with the Mikuni Carb. I spoke to Bill last night and he tells me one of his customer managed to do 20,000miles without problems. I do have some questions about removing the fuel injection and other stuff, is it possible to message you about it?

BTW, nice photo shot of your KLX250, you must do quite a bit of adventure riding. Once the bike is done up, i will be riding up to BKK